1. Field of the Invention
The present invention relates to two-way communications systems and, more particularly, to such systems provided with safeguards against unauthorized system access.
2. Description of the Prior Art
Cable television systems have long been in use in rural areas where television reception by conventional means is made impossible due to the great distance of such areas from the transmitting station. For related reasons, such systems have also been used in areas where reception is difficult due to man-made interference or other impediments. An example of this second category is the metropolitan area of major cities where high-rise buildings often block conventional television broadcasts.
Due to the recent interest in home entertainment centers capable of showing the latest movies or sports events, CATV systems are now generally in demand by both urban and suburban residents. Furthermore, advances in the field of fiberoptics and satellite communications have now made possible the transmission and reception of television signals from distant cities and even countries, thus enabling a viewer to watch more than just those stations which can be received locally by conventional means.
In order to meet the growing demand for CATV and other subscription communications services, many systems have been invented and are known in the art. A typical communications system of this general type includes a program source which transmits simultaneously all of the various audio and video signals along the transmission medium, be it cable, fiberoptic bundle, communications satellite, microwave link, or the like. In the subscriber's home, an up-frequency converter is provided having a tunable local oscillator and a fixed-frequency down-converter. In such a system, the tunable converter is used to select the desired frequency, i.e., program, which may be viewed on the subscriber's television when tuned to a predetermined unused channel.
While such systems have received widespread acceptance, they generally suffer from two major problems. First, the circuit component located in the subscriber's home, namely, the tunable converter, is a relatively expensive part of the system and is often lost, stolen or damaged by the subscriber. Second, such systems are not secure against unauthorized access, since the frequency converters can easily be copied for use by non-subscribers. While this latter problem can be partially overcome by utilizing frequency converters of complicated designs, or by scrambling the transmitted signals at a central location and de-scrambling subsequently, either solution results in significantly increased costs, often to the point of rendering the system economically impractical.
A further security-related problem is the prevention of access by a subscriber to programs for which he is not authorized. For example, a subscriber authorized to receive only those channels showing movies should not be permitted to receive those channels showing sporting events for which he has not paid. Furthermore, a subscriber should receive no service at all unless his account is fully paid. In the event a subscriber is to be disconnected from the system for nonpayment or other reasons, it is also desirable to minimize the cost of such termination.
Several subscription communications systems are known in the art which have attempted to solve one or more of the foregoing problems. For example, U.S. Pat. Nos. 3,886,302 and 4,161,751 both disclose communications systems utilizing a computer or memory at the headend station location to compare subscriber requests with records of payment and authorized program reception. An authorized request results in the enabling of equipment located at the subscriber's home or tap-off location, thereby allowing viewing of the requested program whereas an unauthorized request would not result in enablement of the equipment. The systems disclosed by these patents involve a considerable amount of complex equipment located in the subscriber's home, however, which represents a considerable cost factor and is a decided disadvantage.